1. Field of the Invention
The present invention relates to a wafer stage for use in a semiconductor manufacturing apparatus which attracts and holds a semiconductor wafer.
2. Description of the Related Art
A semiconductor manufacturing apparatus for subjecting a semiconductor wafer to processes of exposing, etching, or the like is equipped with a stage that attracts and fixes the wafer. In processing a wafer by means of this type of semiconductor manufacturing apparatus, the wafer is taken out of a wafer carrier, then carried by a conveyer belt and shifted onto the stage by a handler. The stage is provided with a plurality of vacuum lines. Thus, the wafer placed on the stage is fixed on the stage by vacuum chucks.
It is preferable that wafers should have little warp. Recent wafers are made large in diameter and coated previously with a film for improving their properties. When wafers are formed on their surface with a thick film or subjected to heat treatment at a high temperature, they can warp downward or upward to the extent of tens of micrometers to 250 micrometers.
When there is a warp in a wafer, a conventional vacuum chuck causes a leak error, failing to fully attract the wafer to the stage. For this reason, the subsequent processing cannot be performed. If, although the wafer can be attracted to the stage, the attraction is incomplete, it is difficult to eliminate the warp in the wafer. If the wafer cannot be fixed completely on the stage, various problems will arise, depending on the type of apparatus to which the stage is applied. If, for example, the stage is used in an exposure system, a warped wafer will result in out-of-focus of exposing beams in different positions on the wafer surface. This will reduce the resolution of a pattern formed on the wafer. If, on the other hand, the stage is used in an etching apparatus, the wafer, when subjected to cooling, will be cooled unevenly, depending on places on its surface.